In mammals, injury triggers a complex cascade of cellular and biochemical events that result in a healed wound. Wound healing is a complex dynamic process that results in the restoration of anatomic continuity and function; an ideally healed wound is one that has returned to normal anatomic structure, function and appearance.
Chronically contaminated wounds all contain a microbial flora. These microbes may be indigenous to the patient or might be exogenous to the wound. Closure, or eventual healing of the wound is often based on a physician's ability to control the level of this microbial flora. Infection of wounds by microbes delays the healing process, since the microbes compete for nutrients and oxygen with macrophages and fibroblasts, the activities of which are essential for wound healing. Infection arises when microbes achieve dominance over the systemic and local factors of host resistance. Infection is therefore a manifestation of a disturbed host/microbe equilibrium in favour of the invading microbes. This can elicits a systemic septic response, and also inhibit the multiple processes involved in wound healing. Lastly, infection can result in a prolonged inflammatory phase and thus slow healing, or may cause further necrosis of the wound. The granulation phase of the healing process will begin only after the infection has subsided.
In clinical practice, a diagnosis of infection is often based on the presence of local pain, heat, swelling, discharge and redness, although many clinical indicators, such as inflammation and discharge, are of low predictive value of infection in wounds. The present inventors have found that these clinical indicators of infection are a poor predictor of actual, measured bacterial bioburden in wound fluids. Definitive diagnosis is achieved by microbiological analysis of wound samples. Tissue biopsy provides the most accurate results, but this is an invasive procedure that is difficult to achieve for the majority of wounds. Wound swabbing is the most common wound sampling method used in the United Kingdom, although its clinical value has been questioned. Furthermore, microbiological analysis of wound infection can take 48 to 72 hours, which allows time for infection to develop further if first-line/best-guess treatment is not employed immediately.
There therefore remains a need in the art for methods for the early diagnosis and prognosis of wound infection (elevated bacterial bioburden), and for devices and kits for use in carrying out such methods.
WO-A-03040406 describes a method of predicting or diagnosing clinical infection of a wound comprising measuring the concentration of a marker associated with an inflammatory response in wound fluid, wherein the marker is a fibronectin fragment, a neutrophil protease or a macrophage protease. An elevated level of the marker is said to correlate with increased likelihood of clinical infection. The suggested markers are: a fibronectin fragment, a neutrophil protease or a macrophage protease, for use in the manufacture of a medicament for predicting the likelihood of clinical infection of the wound or for diagnosing clinical infection of a wound. The following markers are listed: elastase, MMP-9, MMP-8, MMP-1, MMP-12 and cathepsin G. Also listed were a collagen propeptide, a collagen telopeptide, a protease inhibitor, plasmin, lactate dehydrogenase, a cathepsin, a cytokine, a peroxidase enzyme, a cortisol free radical or a growth factors. Suitably, the marker is a protease enzyme selected from the group consisting of matrix metalloproteinases (e.g. MMP-9), neutrophil elastase, plasmin, low molecular weight gelatinases and latent or active elastases, interleukin converting enzymes or tumor necrosis factor (TNFa) converting enzymes. The examples describe measuring the activity of the following markers in diabetic foot ulcer fluid: Neutrophil-derived elastase, plasmin, and matrix metalloproteinase. Elevated levels were found in wounds exhibiting signs of clinical wound infection.
WO-A-2004086043 describes a method of predicting or diagnosing clinical infection of a wound comprising measuring the concentration of a marker associated with an inflammatory response in wound fluid, where the marker is a proinflammatory cytokine. An elevated level was found to prognostic of clinical wound infection. The preferred proinflammatory cytokine is TNF-α. Further markers suggested were: Interleukins such as IL-1β, IL-4, IL-6, IL-8, IL-10, IL-18, MCP-1, MCP-2, MCP-3 (monocyte chemoattractant proteins), MIP-1α, MIP-Iβ, MIP-2 (macrophage inflammatory proteins), Interferons IFN-alpha, IFN-beta, and IFN-gamma, GM-CSF (granulocyte/macrophage colony stimulating factor), PF-4 (Platelet factor 4), and RANTES (a member of the chemokine family). The examples describe measuring the activity of TNF-α in diabetic foot ulcer fluid from two patients. The data showed elevated TNF-α in the patient who subsequently developed infection. No measurement of bacterial bioburden in the wounds was carried out.
US-A-2007053962 describes methods of diagnosis or prognosis of a mammalian wound infection comprising the step of measuring the level of at least one cell surface receptor in a sample of wound fluid. The preferred cell surface receptors are Intercellular adhesion molecule-1 (ICAM 1) and Tumor Necrosis Factor Receptor-2 (TNF-R2). The examples present data for venous leg ulcers showing that the levels of both ICAM 1 and TNF-R2 increase with bacterial bioburden by approximately an order of magnitude over the range of bioburden studied.
GB-A-2430031 describes methods for the diagnosis or prognosis of wound infection comprises measuring the level of interleukin-4 (IL-4) in a sample of wound fluid. An elevated level is indicative of wound infection. The example shows positive correlation of measured IL-4 activity to bacterial bioburden in venous ulcer fluid.
US-A-2007053961 describes methods of diagnosis or prognosis of a mammalian wound infection, comprising the step of measuring the level of at least on angiogenic factor in a sample of wound fluid. Suitably, the angiogenic growth factors are selected from the group consisting of acidic fibroblast growth factor (FGF-1), granulocyte colony stimulating factor (G-CSF), basic fibroblast growth factor (FGF-2), hepatocyte growth factor scatter factor (HGF/SF), vascular endothelial growth factor, vascular permeability factor (VEGF/VPF), pleiotrophin, transforming growth factor-[alpha] (TGFα), proliferin, transforming growth factor-[beta] (TGFβ), follistatin, tumor necrosis factor-[alpha] (TNFα), placental growth factor (P1GF), angiogenin, midkine, interleukin-3 (IL-3), platelet-derived growth factor-BB (PDGF-BB), interleukin-8 (IL-8), fractalkine and platelet-derived endothelial cell growth factor (PD-ECGF). The examples show an increase in VEGF level with increasing bacterial bioburden in venous leg ulcer fluids.